Investigation into the dielectric behavior of ferroelectric superlattices formed by pulsed laser deposition

In an attempt to reproduce the functional properties associated with relaxe r electroceramics, pulsed laser deposition has been used to fabricate thin- film capacitor structures in which the dielectric layer is composed of a su perlattice of Ba0.8Sr0.2TiO3 and Ba0.2Sr0.8TiO3. The properties of the capa citors were investigated as a function of superlattice periodicity. The die lectric constant was enhanced at stacking periodicities of a few unit cells , consistent with relaxer behavior. However, enhancement of the dielectric constant was found to be associated with high dielectric loss. Analysis of the imaginary permittivity as a function of frequency shows that fine-scale superlattices conform to Maxwell-Wagner behavior. This suggests that the o bserved enhancement of the real part of the dielectric constant is an artef act produced by carrier migration. A comparison of this data with that alre ady published on dielectric superlattices suggests that previous claims of an enhancement in dielectric constant may also be due to the Maxwell-Wagner effect. The onset of Maxwell-Wagner behavior was attributed to increasing density of defect zones associated with discontinuities in the superlattice structures. In an attempt to exaggerate the influence of such zones, delib erate delays between deposition of successive dielectric layers were introd uced. This resulted in reproduction of several features normally associated with relaxors: enhancement of dielectric constants by over an order of mag nitude; strong frequency dispersion around and below T-m; migration of T-m with frequency. However, these features were again associated with relative ly high loss. (C) 2000 Kluwer Academic Publishers.